Promotion effect of nanosized Pt, RuO2 and NiOx loading on visible light-driven K4Ce2M10O30 (M=Ta, Nb) photocatalysts for hydrogen evolution from water decomposition

Mengkui Tian
Research Center for Combustion and Environment Technology, Shanghai Jiao Tong University

Wenfeng Shangguan
Research Center for Combustion and Environment Technology, Shanghai Jiao Tong University

Jian Yuan
Research Center for Combustion and Environment Technology, Shanghai Jiao Tong University

Shijie Wang
Geochemistry Institute of Chinese Academy of Sciences

Ziyuan Ouyang
Geochemistry Institute of Chinese Academy of Sciences

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     Last modified: February 15, 2006

Abstract
The development of hydrogen as a renewable energy is well believed to be a potential way to solve the current energy and environmental problems. The photocatalytic decomposition of water using solar energy is one of the most promising ways to develop hydrogen energy. The most important work in photocatalytically decomposing water into H2 is to develop semiconductor photocatalysts capable of responding to visible light and possessing high quantum yield.
In present paper, novel metal oxide photocatalysts K4Ce2M10O30 (M=Ta, Nb) were synthesized by conventional high temperature solid state reaction. The photocatalysts have an appropriate band gap energy ca. 1.8 - 2.3 eV (corresponding to absorption edge of 540 ~ 690 nm) and excellent chemistry potential level for utilization of solar energy to evolve H2 and O2 from aqueous solutions containing either sacrificial electron donor (Na2SO3) or acceptor (AgNO3) respectively under visible light irradiation (λ> 420 nm) without any co-catalyst. The activity was greatly promoted by loading nanosized Pt, RuO2, NiO and NiOx (derived from the treatment of NiO reduction-oxidation). The amount of H2 evolution in Na2SO3 solution under visible light irradiation (λ> 420 nm) for 4 h on NiOx-loaded K4Ce2M10O30 reached 135 μmol (M=Ta) and 51 μmol respectively, which is about 4~7 times of that loaded with Pt and RuO2, and 10~15 times of that without any loading. Through SEM and TEM study, it can be seen that these loading metal or metal oxides were dispersed on the surface of photocatalysts K4Ce2M10O30 (M=Ta, Nb) in diameter of 20-50 nm nano particles. Especially, the loaded NiOx formed the metal Ni and metal oxide (NiO) double layer structure in order. The reasons for the increasing activities after loading these nanosized particles might be attributable to facilitate electron migrating from the conduction band of K4Ce2M10O30 (M=Ta, Nb) to the Pt, RuO2 and NiOx nanoparticles, which functioned as H2 production sites on the surface of catalysts. The parallepiped (tunnel) surface structure of K4Ce2M10O30 (M=Ta, Nb) was beneficial to the formation of “nest” where nanoparticles of Pt, RuO2 and NiOx were strongly associated, improving the photocatalytic activity greatly. Furthermore, the double-layered structure of nickel formed by the treatment of reduction-oxidation was easier to assist the electron transferring from photocatalysts to co-catalysts, and retain the back reaction of H2 and O2 on surface. Therefore, it showed the highest activities for H2 evolution compared with current other loadings.